Here is what I think.

Eddie,
91FX + Karl's header + ES carbon? Isn't it higher than YS 110?


For the need of 90 size 2-stroke engine, I went with OS 91SX-H. If I had enough $$, I would have gone with YS 91ST.

Remote needle of OS was one reason that I chose to use 91SX-H. Since I am using 30% nitro for YS engines, I can use the same fuel in the 91SX-H. I bought it slightly used & cheap. Tried it with 91FX muffler, Macs standard header & a tuned pipe. 91SX-H turns 15x8 @10K with 20 something % nitro. I can still get more rpm, but it is still running better than 91AC that I have.

Right now, I have a wrap around-header by Karl Mueller ready to go.
The set up worked fine with a Perry VP-30 last time I tried a few months ago on a stand. (Fuel tank moved up and downabout 12" without any throttle changes).

For a Webra 80 at $350, I would go with a YS 110. It is lighter than YS 91AC/FZ and similar price with the Webra 80. 4-stroke also uses less fuel.